388 Results of the Competition of 1874, 
difference which has shown itself so obviously in these localities 
may be found in some varieties sufficiently pronounced to free 
them altogether from the attack of the disease. 
I have made a microscopical examination of the leaf epi- 
dermis of the six kinds of potato with the view of ascertaining 
whether any character could be detected which might explain 
the freer access of the spores to one variety than to others. The 
upper surface of the leaf is sparsely covered with short curved 
hairs, which rise irregularly from the epidermal cells. These 
hairs are almost entirely confined on the under surface to the 
veins and their various and minute ramifications. The epider- 
mis of the spaces between the veins gives off some scattered 
glandular hairs, composed of a small round transparent ball 
supported on a short jointed stalk. In none of the varieties are 
these hairs sufficiently numerous to prevent the spores lodging 
on the surface of the epidermis. The leaves of the two early 
potatoes are most densely covered with both kinds of hairs. I 
found no appreciable difference in the four late varieties. 
In looking, then, at the conditions natural or applied under 
which the crops were grown, we may hope to find in them some 
help towards understanding the remarkable differences that are 
exhibited in the tables. 
We may at once dismiss the soils from our consideration, 
seeing that the disease was severe as well on the peat of Con- 
naught as on the loam of Ayr and South Wales, and the stifll 
clay of Exeter, while similar soils in other localities were free 
from the malady. 
The information supplied by growers of potatoes led Mr. 
Jenkins, in his recent Report, to suggest the probability of the 
fungus which produces the disease being parasitic during part ol 
its life on some other cultivated crop. As parasitic fungi, which, 
as far as the knowledge of them has been ascertained, might be 
related to the Peronospora of the potato, had been found on wheat' 
and clover,t and as the potatoes that escaped disease, in the re- 
turns on which his report was based, followed green crops, Mr 
Jenkins recommended that observations should be instituted witi 
the view of determining whether potatoes following wheat, an( 
especially clover, were more liable to disease. Professor Farlov 
has, as wo have seen, recommended the prosecution of simila 
inquiries in America. Last year's experimental crops do no 
give any support to the suggestion of Mr. Jenkins. In tw< 
localities, Staffordshire and Lancashire, the potatoes foUowef 
clover, and though in both jplaces disease was found to hav* 
* ' Journal of the Koyal Agriculliiral Society,' second series, vol. viii. (1872 
p. 2V6. 
t Ibid., vol. X. (1874), p. 515. 
